Ultrasonic remote control systems have for years been a popular control medium for television receivers and are well known in the art. Such systems normally include a transmitter containing rods which when struck produce a predetermined acoustic frequency and a transducer in the receiver for converting these control signals into corresponding electrical signals. Noise immunity is normally achieved by requiring that a control signal have a constant amplitude for some fixed period of time. Detection circuitry usually includes tuned circuits equal in number to the actuation frequencies adapted so that a selected frequency will cause resonance within a corresponding circuit. For design variations any of the activation frequencies may be changed by merely changing the length of the struck rod and the components of the corresponding tuned circuit.
Ultrasonic remote control systems can be designed and fabricated in an integrated circuit by employing digital techniques. As before, several predetermined frequencies are employed to activate corresponding functions. Generally, a clock is coupled to a counter which samples the incoming signal to determine its frequency and noise immunity is achieved as for the conventional circuit. The digital systems actually count the actuation signal frequency in predetermined timing intervals. The system responds to these various counts and the actuation frequencies once selected must remain fixed. A problem which arises is to provide for some variation in digital remote control systems while taking advantage of the simultaneous fabrication and interconnection offered by integrated circuit technology. A digital IC system once formed will only respond to the predetermined frequencies which give the proper count during the timing interval.
The principal advantage of an integrated circuit is that once the design format is determined a cost savings can be gained with a high volume production of units. For television receivers the number of remote control units is considerably smaller than the number of total television sets produced. In addition providing a variety of remote control systems would again diminish the number of production units and could reach a point where the question of whether or not an integrated circuit should be used would arise.
An additional cost consideration arises from the number of pins required to interface the integrated circuit with the remainder of the electronic system. The cost vs. number of pins required for an integrated circuit package is not a linear function and in some cases one more pin can add considerable cost because a much larger package may have to be used. Therefore if one wishes to provide design variety with an integrated circuit, and maintain cost effectiveness, the circuit should have a minimum number of output pins.
Applicants' invention resolves these problems by including logic gates which establish control for differing functions depending upon an outside logic level selection. It provides the desired design variation on a single chip to take advantage of high volume production and utilizes common output pins to retain the advantages of a package with a smaller number of output pins.